The present invention relates to electron tubes, and particularly to a high power electron tube for use in VHF and UHF operation. The envelope of the electron tube includes both metallic and insulating rings sealingly interconnected with one another. The metallic rings serve as lead-out conductors for electrically connecting the electrodes inside the tube envelope to external terminals. An improved anode structure forms a portion of the tube envelope.
U.S. Pat. No. 3,327,156 to Gerlach issued on June 20, 1967 describes a high power electron tube of ceramic-metal construction that utilizes a compressible annular contact member in the form of helically-wound wire disposed between the anode of the tube and the end surface of an adjacent conductive annular ring that comprises a section of the tube envelope. The disclosed structure provides a means of manufacturing electron tubes in a plurality of subassemblies without extensive welding, soldering or brazing. The helically-wound wire provides both a highly conductive electrical path between the anode and the adjacent conductive annular ring as well as a means of reducing the effect of differential expansion between the anode and the ceramic elements of the tube envelope. The structure described in the Gerlach patent is an improvement over the prior art electron tube structures which are assembled by means of peripheral welded or brazed seams between adjacent conductive members. In such prior art structures, alternating currents tend to flow near the outermost surfaces of the metal parts throughout the major portions of the paths from the internal electrodes to the external tube terminals and introduce high resistance into the tube connections with the external circuitry. Such a tendency is known as skin effect. The high resistance connections may be detrimental to proper operation of the tube. While the helically-wound wire contact member disclosed in the Gerlach patent provides advantages over conventional prior art tube interconnections, the helically-wound wire contact member tends to fatigue after a period of time due to mechanical and thermal effects and the electrical contact between the anode and the adjacent conductive ring deteriorates. As a result, an intermittent decrease in the power output of the tube occurs. Additionally, internal arcing across the contact member may occur resulting in a localized increase in tube temperature and a failure of a ceramic element. Such a failure requires the replacement of the tube.
U.S. Pat. No. 3,287,597 to Smith, issued on Nov. 22, 1966 shows a tube structure in which the wall thickness of the copper anode is reduced at the sealing edge to withstand the forces caused by the different expansion characteristics of the copper anode and the ceramic portion of the envelope wall. The reduced thickness anode wall forms a sealing ring which comprises a portion of the vacuum envelope. The sealing ring of the Smith structure must be thick enough to maintain the vacuum integrity of the envelope and high enough to provide the flexibility required to withstand the expansion difference between the anode and the ceramic.